Interpretive Summary: Consumer demand and changes in government regulations are requiring an increase in non-chemical control of insect pests. A sustainable alternative to chemical control is to make use of natural biological controls. In this study we investigated the addition of a compost mulch to increase the ability of natural insect predators to control insect pests in an apple orchard. Composted poultry manure was added as a mulch to a newly planted apple orchard and compared with a herbicide treated control. The abundance of insect predators as measured with pitfall traps and their ability to control an insect pest with artificially introduced codling moth larvae were compared. It was found that the compost mulch increased the abundance of predators but did not increase the degree of biological control of codling moth due to differences in preferences for habitat characteristics that existed in the herbicide treatment. These results will be used by ecology and pest management researchers working to increase levels of biological control in orchards and other agricultural systems through habitat manipulation.

Technical Abstract:
Augmenting generalist predator populations in new apple (Malus domestica Bork) plantings could potentially aid in the establishment of balanced orchard ecosystems that are less susceptible to pest outbreaks. Habitat can be an important factor in retaining predators in a system and can affect predator efficiency. We investigated the potential of increasing a complex of generalist ground-dwelling predators and enhancing biological control in a young 'Golden Delicious' apple orchard through ground habitat manipulation. We modified the orchard floor with four comparative habitat treatments: 1) detritus-rich compost mulch layer, 2) detritus-free synthetic mulch layer, 3) herbicide-treated vegetation thatch, and 4) bare soil with vegetation hand-removed. Relative abundances of predators and alternative prey in the habitats were measured with pitfall trapping throughout the growing season. Predation was measured using sentinel C. pomonella larvae and directly observed in night experiments. Throughout the season the compost mulch treatment consistently supported significantly greater densities of alternative prey resources for predators, and generalist predators were more abundant in the compost mulch than the other habitats. The predator complex was positively correlated with alternative prey in the compost mulch habitat. However, biological control of C. pomonella was significantly lower in the compost mulch than in the herbicide-treated thatch habitat. Our study revealed that enhancement of generalist predators on the orchard floor is possible through the addition of a prey-rich organic mulch, but suitable habitat may be more important than alternative prey for biological control by ground-foraging generalist predators.